Synthesis and Coordination Chemistry of 2-(Di-2-pyridylamino)pyrimidine; Structural Aspects of Spin Crossover in an FeII Complex

Abstract

2-(Di-2-pyridylamino)pyrimidine (L), a potentially ditopic tetradentate ligand, was synthesized from commercially available di-2-pyridylamine and 2-chloropyrimidine. Despite being capable of bridging two metal atoms with bidentate chelation of both metal centres, L prefers to chelate or bridge through the more basic pyridyl donors of the di-2-pyridylamine moiety. Mononuclear trans-[Fe(NCS)2(L)2] and [Cu(L)2(H2O)](BF4)2·H2O complexes, and a discrete [Ag2(L)4](PF6)2 metallo-macrocycle, were isolated and structurally characterized by X-ray crystallography. A mononuclear palladium complex [PdCl2(L)]·(solvate), where solvate = 1/2H2O or CH2Cl2, was also readily obtained in 71 % yield. One example of the ligand acting as a bis(bidentate) bridging ligand was observed in a dinuclear [(PdCl2)2(L)]·3/4H2O complex that was obtained only in very low yield (~3 %) from the reaction that produced [PdCl2(L)]·1/2H2O. trans-[Fe(NCS)2(L)2] undergoes a temperature-dependent high-spin–low-spin crossover at ~205 K that was observed by X-ray crystallography and magnetic measurements, and attempts were made to understand the structural basis of this process. Despite efforts to isolate examples of L bridging two iron(ii) centres, only the mononuclear trans-[Fe(NCS)2(L)2] species could be obtained.